Project 1: Interference with the Androgen Receptor and Its Ligands in Recurrent Prostate Cancer In spite of earlier detection of prostate cancer, many men succumb to prostate cancer that can be palliated but not cured by androgen deprivation therapy. When prostate cancer recurs during androgen deprivation therapy, androgen receptor protein and androgen-regulated genes are expressed at levels similar to that of androgen-stimulated prostate cancer. Many laboratories have focused upon methods of androgen receptor activation that do not require androgens since circulating testicular androgens are low or undetectable after medical or surgical castration and the effects of adrenal androgens have been blocked by antiandrogens. During the last 4 years of our P01, we demonstrated that recurrent prostate cancer expresses high levels of androgen receptor protein that is usually wild type and recurrent prostate cancer tissue contain levels of testosterone and dihydrotestosterone capable of activating the androgen receptor. Prostate-specific antigen, the classic androgen-regulated gene, is expressed at similar tissue levels in recurrent and androgenstimulated prostate cancer. We will test the hypothesis that recurrence of prostate cancer during androgen deprivation therapy can be prevented or delayed by preventing the accumulation of tissue androgens and/or suppressing the androgen receptor. In Aim 1, we will define the mechanism of generation of tissue levels of androgens sufficient for androgen receptor activation using clinical specimens and prostate cancer cell lines and xenografts. Once the important androgen producing enzymes have been identified, they will be inhibited in Aim 2 using antisense technology. In addition, androgen degradation will be enhanced by transfecting androgen-degradative enzymes using the lentiviral vector system. In Aim 3, we will use an androgen receptor dominant negative delivered using the lentiviral vector system to suppress androgen receptor function. At the conclusion of Project 1, prostate cancer recurrence in a xenograft model will be prevented or delayed by a two-pronged attack to remove ligand from, as well as suppress, the androgen receptor.